Display paging receivers have been gaining wide acceptance because they provide improved informational benefit to a user compared to tone only pagers. Both numeric display pagers, which are used to present numeric data such as telephone numbers, and alphanumeric display pagers, which are used to present alphanumeric data such as "CALL HOME AT 444-9847", are available in today's market.
LCD displays are generally used to present for viewing the received messages because they provide unlimited flexibility in formatting the presentation of the messages. Examples of such flexibility include single or multiple line displays, and seven or fourteen segment character formats. A benefit of LCD displays has been the low drive power requirements, critical in a portable product having an extremely limited battery capacity. However, LCD displays are only viewable where the ambient light levels are adequate to illuminate the display. LCD displays are unviewable in low light level conditions, such as in dark rooms or in the evening and nighttime hours.
Various methods of overcoming the low light level viewing of LCD displays have been proposed. The simplest method has been to provide a light, such as incandescent lamp or electroluminescent back plane, operable by a switch to illuminate the display. The light illuminates the display for the time the switch continues to be actuated by the user. While this has provided acceptable display illumination, it has been very inconvenient when long messages must be reviewed.
Methods have been proposed to overcome the problem of manually operating the light for display illumination. One such method has been to provide a photosensor for monitoring the ambient light level, automatically turning on the light any time a message has been received and displayed. Such a method adds complexity to the design, and while the method overcomes the problem of manually operating the light switch to provide display illumination, the method has added substantially to the current drain of the receiver.
There are times when messages that have been received may be deferred for reviewing until a later time. In such instances, it is desirable to have the display lighting operational only as long as the display is activated and only when so initiated by the user. There are other times when status messages, such as the number of messages stored and memory full indications are presented on the display which the user may want to review. Again, when display illumination is required, it is desirable to provide the illumination only when so initiated by the user.